1. Field of the Invention
The present invention relates to a multi-metal coplanar waveguide (CPW) which can enhance fidelity and minimize loss of a CPW by designing a ground line in various shapes when a CPW transmission line is designed using multi-layer interconnection CMOS technology in order to apply to the design of a CMOS IC operating at ultra high frequency.
2. Discussion of Related Art
In design of a conventional CPW using multi-layer interconnection CMOS technology, a method of designing an uppermost metal layer to have a ground-signal-ground line structure has been used. In addition, a method of shielding the CPW by inserting a ground line below the CPW as a lowermost metal layer in order to reduce a CPW loss caused by a silicon substrate and a method of shielding the CPW using patterned ground lines have been used. Moreover, a method of connecting ground lines of uppermost and lowermost layers using intermediate metal layers and via holes has been widely used.
In the CPW, a transmission signal is sensitive to a shape and pattern of a ground line as well as the width of a signal line and the distance between the signal line and ground lines.
As CMOS technology has rapidly developed, RFICs operating at radio frequency have been actively commercialized and recently attracting attention as technology applicable to the higher millimeter wave band. In millimeter wave band IC design, a transmission line is a basic passive element transmitting signals and having a capacitance and an inductance.
However, when the transmission line and the CPW are designed by multi-layer interconnection CMOS technology, because the distance between the signal line and ground lines cannot be large, they have low fidelity and a signal is largely attenuated by a conductive silicon substrate.